cides may lead to a sequence of events over two seasons, 

 beginning with premature defoliation in the fall and pro- 

 gressing to decreased fruit bud viability, decreased set and 

 decreased production. It thus appears that fungicides have 

 positive effects on fruit production which go beyond the 

 direct benefits of controlling common diseases. 



Pesticide Treatment in Scab-resistant Blocks 



In order to study the effects of pesticides on the ecol- 

 ogy of orchards, a block of SRCs in each of four commer- 

 cial orchards was selected and each was partitioned into 

 four sections. Treatments were divided randomly among 

 the four sections; 1) fungicide, insecticide and miticide 

 applications made using first-level IPM methods; 2) fun- 

 gicide applications made using first-level IPM, and arthro- 

 pod management done using second-level IPM; 3) no fun- 

 gicides, and arthropod management done using first-level 

 IPM; 4) no fungicides, and arthropod management done 

 usingsecond-level IPM. The second-level IPM techniques 

 used were described earlier in this issue, except that pesti- 

 cide-treated spheres were used to manage apple maggots. 



Results and Discussion 



Fungicide treatment and arthropod treatment each had 

 a significant effect on the total amount of pesticide used for 

 the season (p 0.05). Table 1 shows that on average 4.2 

 dosage equivalents (DEs) of fungicide were applied in fun- 

 gicide-treated sections. The rest of each block received no 

 fungicides. The first-level IPM sections of blocks received 

 5.3 and 0.5 DEs of insecticides and miticides, respectively, 

 while the sections under second-level IPM received 3.5 and 

 0.3 DEs, respectively. 



As would be expected, omitting fungicides had a sig- 

 nificant effect on sooty blotch and flyspeck (Table 1). The 

 summer disease incidence was much higher in the sections 



where no fungicide was used. The arthropod treatment, 

 either first-level or second-level IPM, did not have a sig- 

 nificant effect on summer disease, nor was there any inter- 

 action between the fungicide treatments and arthropod treat- 

 ments (data not shown). 



There was also a significant negative correlation be- 

 tween the number of DEs of fungicide applied over the sea- 

 son and the incidence of sooty blotch (r=-0.83) and fly- 

 speck (r=-0.87), which means that the more fungicide that 

 was applied'Over the entire growing season, the lower was 

 the summer disease incidence. The DEs applied over the 

 entire season had higher correlation values with summer 

 disease than did the DEs after June 15, indicating that the 

 entire season's fungicide program has more effect on dis- 

 ease than the summer fungicide applications alone. 



The application of fungicides also was significantly 

 related to European red mite populations. DEs of fungi- 

 cides applied after June 15 were positively correlated with 

 European red mite populations (r=0.62), indicating that 

 more applications of fungicide in the summer were related 

 to higher red mite populations in the blocks, as illustrated 

 in Figure 1. The DEs applied for the season were not as 

 highly correlated (r=0.27). The statistical strength of these 

 relationships mdicates that other factors are affecting the 

 red mite populations, as would be expected, but fungicides 

 do appear to play a role in growth of red mite populations. 

 The populations of the other major pest mite in orchards, 

 the two-spotted mite, were very low, approaching or at zero 

 in most orchards. 



The major predator mite observed in these orchards 

 was the yellow mite. Fungicide use correlated with a sig- 

 nificantly lower yellow mite populations. While some or- 

 chards had few if any yellow mites, in those orchards with 

 these predators, populations were lower in fungicide-treated 

 sections. 



Neither arthropod treatments nor fungicide treatments 

 had significant effects on several other foliar pests and ben- 



Table 2. Percent of fiiiit with sooty blotch and flyspeck damage, and percent of leaves with mites and mite 

 predators, from sections of four blocks of scab-resistant apple cultivars.* 



Treatment 



Sooty blotch 



Fly speck 



ERM 



TSM 



AF 



YM 



Fungicide 

 No fungicide 



0.3 



11.7 



0.7 a 

 13.4 b 



29.8 a 

 21.5 b 



0.1 

 0.0 



4.2 a 

 3.9 a 



3.9 a 

 10.0 b 



Within columns, means not followed by the same letter are significantly different at odds of 19:1. 

 ERM=European red mite; TSM=Two-spotted spider mite; kV=Amblysehts fallacis; YM=yellow mite. 



Fruit Notes, Winter, 1995 



17 



